In this proposal, we seek to continue to demonstrate the importance of the application of the shift reagent (SR) technique which we have developed to the 23Na and 39K NMR spectroscopy of tissue. The use of SR allows the discrimination of the transmembrane NMR signals of biological metal cations. This, in turn, provides for the potential quantitation of cation concentration and the continual monitoring of transmembrane transport. We propose to synthesize and test new SR, seeking increased effectiveness, compartimental specificity, etc. We also propose to test new relaxation reagents (RR). We intend to carry out careful measurements of the NMR-visibility of the cation signals from different compartments in different tissues. We wish to continue to explore the nature of the transport processes we can observe by this approach and their biological and medial consequences. Thus, we plan to extend our studies of passive and active Na+ and K+ transport in human erythrocytes and yeasts. With the latter, we want to test what we think is a newly found relationship between ion transport and phosphorus metabolism. We intend to continue our studies of the perfused, beating rat heart. We can monitor the Na+ -loading of the heart myocytes after a number of different interventions. Combination SR and RR experiments will allow us to investigate the apparent additional consequences of these interventions on the interstitial and vascular spaces. We also propose new SR experiments on the in vivo rat brain. These promise the possibilities of assaying the permeability of the blood-brain barrier (BBB), the relative volumes and ion concentrations of the different brain compartments, and the monitoring of transport of Li+ across the BBB. Our experiments mostly employ the standard ex vivo and in vivo methodology of high-resolution NMR, at high fields (greater than or equal to 7 T), of stable magnetic isotopes present in natural abundance. This work involves aspects of physics, physical and inorganic chemistry, biochemistry, biophysics, and physiology, and has ramifications in the study of a number of pathological conditions including heart disease and affective disorders.